1. Field of the Invention
This invention relates to needle-suture combinations and more particularly to needle-suture combinations comprising fluid swellable sutures and surgical needles attached to the suture by swaging so that the needle is removable by a force of from about 3 to 26 ounces.
2. Description of Prior Art
The concept of a needle-suture combination having a removable swaged needle was first described in U.S. Pat. No. 3,890,975. Such a needle-suture combination is more convenient for the surgeon since after completing the suturing procedure, the needle can be removed from the suture by a quick tug, whereas conventional sutures require the needle to be cut from the suture.
Subsequent to U.S. Pat. No. 3,890,975, several techniques have been proposed for providing needle-suture combinations of different types and compositions with removable needles. These are described, for example, in U.S. Pat. Nos. 3,875,946; 3,926,164; 3,943,933; 3,949,756; 3,963,031 and 3,981,307.
The methods described in the above patents provide needle-suture combinations having suture pull-out values within the desirable range at the time of manufacture. With suture materials that are relatively dimensionally stable under normal storage conditions, the sutures will retain a pull-out value within the desirable range until the time of use in the operating room. With certain fluid swellable sutures, however, particularly collagenous sutures including both natural collagen strands called "gut" and extruded collagen, there is considerable variation in the volume of the suture with varying moisture content and therefore, a needle-suture combination of these materials may have substantially different suture pull-out values at different moisture contents.
The problem of variable suture pull-out values is particularly acute with respect to needle-suture combinations utilizing collagenous sutures which are wet packed and stored in hermetically sealed envelopes containing a fluid such as an alcohol-water solution to maintain the suture in a pliable state. If the needle-suture combination is manufactured to have a suitable pull-out value when the collagenous material is in a dry state, it may have too high a pull-out value after suture has absorbed water from the aqueous alcohol solution and expanded within the swaged junction of the needle. Conversely, if the needle-suture combination is manufactured to have a suitable pull-out value when the collagenous material has a high moisture content, it may have too low a pull-out value or may not hold together at all if it is allowed to dry out before use.
The difficulty associated with the preparation of controlled release fluid swellable sutures was recognized in U.S. Pat. No. 3,924,630 where it was suggested to dimension the needle opening to provide in the swaged portion of the needle a cross-sectional area equal to from about 150 to about 250% of the cross-sectional area of the suture when the suture was in nonswollen state. The excess volume in the needle opening was discovered to allow for expansion in volume of the suture due to an increase in moisture content without a major increase in suture pull-out value. It has now been discovered, however, that suture pull-out values may decrease to less than preferred levels when a moist suture is allowed to dry and the volume of the suture decreases. The present invention is an improvement over the method and product of the '630 patent which reduces the variability of suture pull-out values resulting from variations in the moisture content of fluid swellable sutures.
It is accordingly an object of the present invention to provide an improved method for attaching needles to fluid swellable sutures whereby the suture pull-out value does not vary beyond acceptable limits with changes in suture fluid content. It is a further object of the present invention to provide a method for attaching needles to catgut sutures so that the suture pull-out value is within the range of 3 to 26 ounces regardless of suture moisture content. It is a yet further object of this invention to provide improved needle-suture combinations comprising fluid swellable sutures with a drilled needle attached thereto by swaging and characterized in that the needle may be removed by a force of 3 to 26 ounces regardless of the extent to which the suture is swollen by presence of moisture. These and other objects of this invention will be apparent from the ensuing description and claims.